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Modifying just the positive feed to solenoid and starter solves only half the problem. All current has to come back to negative after leaving positive terminal. Modified (read BEEFED UP) cable from negative terminal of the battery to engine case and frame is a must as well.
I had 2 hot starts on my2012 before the mod and not 1 since, 3.5 years ago.

Modifying just the positive feed to solenoid and starter solves only half the problem. All current has to come back to negative after leaving positive terminal. Modified (read BEEFED UP) cable from negative terminal of the battery to engine case and frame is a must as well.
I had 2 hot starts on my2012 before the mod and not 1 since, 3.5 years ago.

Not true.

I'm not an electrical engineer but from experience with re-wiring a lot of cars and motorcycles over the last 40 years, and also re-wiring my old house last year, the ground wire does not need to be the same size as the positive (this is according to the building code).

I'm not an electrical engineer but from experience with re-wiring a lot of cars and motorcycles over the last 40 years, and also re-wiring my old house last year, the ground wire does not need to be the same size as the positive (this is according to the building code).

Hopefully, someone who is an EE can enlighten us.

I am an EE and this is not a ground wire. It is commonly referred to as EARTH wire, but in automotive applications that is just a figure of speech. In AC circuits ground wire is a safety wire that exists for protection of equipment and personnel (yes, strange, but in that order). Its a third wire in any single phase system or a 4th wire in any 3phase system and under normal circumstances is not part of any active electrical circuit, but there to provide safe path for current to earth in case of a major malfunction.

DC circuits have feed wire and return wire ( not using words positive or negative because lots of non-automotive applications use negative feed amd positive return). Sometimes DC circuits do use ground wire in addition to feed and return wires for electrical potential reference and secondary safety.

In automotive applications there are 2 wires that complete a circuit to any analog device (non data circuits), like solenoid and starter, for example. Beefing up the feed wire will alleviate thermal variations of conductor resistance in that half of the circuit, but the problem on the return side will remain the same (hence my statement about solving only one half of the problem in my previous post). Thermally Insulating the starter motor will definitely help as well, for same reasons, but I, for one, chose not to do that part because I have not experienced a hot start again after doing just wire upgrades. YMMV

I am an EE and this is not a ground wire. It is commonly referred to as EARTH wire, but in automotive applications that is just a figure of speech. In AC circuits ground wire is a safety wire that exists for protection of equipment and personnel (yes, strange, but in that order). Its a third wire in any single phase system or a 4th wire in any 3phase system and under normal circumstances is not part of any active electrical circuit, but there to provide safe path for current to earth in case of a major malfunction.

DC circuits have feed wire and return wire ( not using words positive or negative because lots of non-automotive applications use negative feed amd positive return). Sometimes DC circuits do use ground wire in addition to feed and return wires for electrical potential reference and secondary safety.

In automotive applications there are 2 wires that complete a circuit to any analog device (non data circuits), like solenoid and starter, for example. Beefing up the feed wire will alleviate thermal variations of conductor resistance in that half of the circuit, but the problem on the return side will remain the same (hence my statement about solving only one half of the problem in my previous post). Thermally Insulating the starter motor will definitely help as well, for same reasons, but I, for one, chose not to do that part because I have not experienced a hot start again after doing just wire upgrades. YMMV

Thanks! I assume if we were to only add additional ground to somewhere in the chassis that fed back to the battery (ie somewhere on the rear subframe to the negative terminal) we would have some difference in potential and create a bit of a ground loop possibly causing noise in some circuits. So it would be ideal to upgrade/add to the whole length of the existing ground. Is that correct?

Also - just for completeness some rare older automotive applications and tractors and such will use a positive "ground" where the positive cable is connected to the chassis and the negative cable runs straight to the devices. This was standardized long ago to eliminate confusion and increase safety, but I'm sure you knew that.

I've worked on so many old cars over the years that used a smaller wire from batt negative, that I always figured it was normal.

I did notice that starting with the 2015 1100-TV4 and RSV4-RR/RF bikes, Aprilia increased the size of the negative ground wire from the batt to the crankcase.
The size wire they are using now is in between the old 8-gauge and a super thick 6-gauge (maybe a 7-gauge ?).

Installing the heavier negative wire from the new bikes was the first thing I tried on the old, but it didn't help.
The p/n for that thicker negative wire is 2D000158

Originally Posted by surfmonster

I am an EE and this is not a ground wire. It is commonly referred to as EARTH wire, but in automotive applications that is just a figure of speech. In AC circuits ground wire is a safety wire that exists for protection of equipment and personnel (yes, strange, but in that order). Its a third wire in any single phase system or a 4th wire in any 3phase system and under normal circumstances is not part of any active electrical circuit, but there to provide safe path for current to earth in case of a major malfunction.

DC circuits have feed wire and return wire ( not using words positive or negative because lots of non-automotive applications use negative feed amd positive return). Sometimes DC circuits do use ground wire in addition to feed and return wires for electrical potential reference and secondary safety.

In automotive applications there are 2 wires that complete a circuit to any analog device (non data circuits), like solenoid and starter, for example. Beefing up the feed wire will alleviate thermal variations of conductor resistance in that half of the circuit, but the problem on the return side will remain the same (hence my statement about solving only one half of the problem in my previous post). Thermally Insulating the starter motor will definitely help as well, for same reasons, but I, for one, chose not to do that part because I have not experienced a hot start again after doing just wire upgrades. YMMV

Thanks! I assume if we were to only add additional ground to somewhere in the chassis that fed back to the battery (ie somewhere on the rear subframe to the negative terminal) we would have some difference in potential and create a bit of a ground loop possibly causing noise in some circuits. So it would be ideal to upgrade/add to the whole length of the existing ground. Is that correct?

Let's just stick to using words "positive" and "negative" wen it comes to automotive electrics. There is no ground connection on any vehicle, at least not on the ones that move on rubber tires.
Creating an additional negative terminal would need to be on engine case first, then on the frame or sub-frame. It will not really create any noticeably adverse effect, but will be a hassle and an additional potential point o failure to worry about. Doubling up on the negative wire from negative battery terminal to existing connection lug on the LH front side of the engine and upgrading existing jumper from engine to the frame is quite adequate, or replacing it all together with some #2 AWG flexible welding wire. This is, of course, in addition to doing the same on solenoid and starter connections on the positive side.

This thread is all about cheap and effective solution to this problem and Amauri's solution is cheap and effective, but it needs to be done on both sides of wire runs with adding 12AWG or 10AWG runs to existing wiring.

If you are handy with tools and wiring, a more expensive, and perhaps, effective way is to replace existing positive and negative feeds with some beefy welding wire, with proper crimp clamps and heat shrink. It would probably cost $20-$30 and a day of work to make it DIY from scratch if you have the tools and to install it.

Also - just for completeness some rare older automotive applications and tractors and such will use a positive "ground" where the positive cable is connected to the chassis and the negative cable runs straight to the devices. This was standardized long ago to eliminate confusion and increase safety, but I'm sure you knew that.

I did not know that, but I am happy to learn something new every chance I get. I wonder if those were "electric start" with battery type or manual start magneto-powered type and how they protected equipment from galvanic reactions every time they plowed or reaped things out of the ground..... or from killing batteries every time.

I've worked on so many old cars over the years that used a smaller wire from batt negative, that I always figured it was normal.

I did notice that starting with the 2015 1100-TV4 and RSV4-RR/RF bikes, Aprilia increased the size of the negative ground wire from the batt to the crankcase.
The size wire they are using now is in between the old 8-gauge and a super thick 6-gauge (maybe a 7-gauge ?).

Installing the heavier negative wire from the new bikes was the first thing I tried on the old, but it didn't help.
The p/n for that thicker negative wire is 2D000158

Just out of curiosity - was there a negative feed direct to starter on those old cars or were they using just a short jumper from negative terminal to the body/chassis?
Heat build up is really a non-issue under the hood of a car but a very considerable issue with our bikes, especially in casual street riding. I will stick a thermal probe one day between the frame and engine case to see what temperatures those wires really sit in during an average commute to work. The outside of my frame routinely gets too hot to touch and hold for more than a second or 2, especially in the summer.

I did not know that, but I am happy to learn something new every chance I get. I wonder if those were "electric start" with battery type or manual start magneto-powered type and how they protected equipment from galvanic reactions every time they plowed or reaped things out of the ground..... or from killing batteries every time.

Most to your point - they found the positive chassis systems corroded the body of the vehicle more quickly.

A family friend has an old (approaching ancient) tractor with positive chassis connections and it is electric start if I remember correctly. It is still used on his farm to this day, so as that link notes it may not be ideal, but it can work for quite some time.

Just out of curiosity - was there a negative feed direct to starter on those old cars or were they using just a short jumper from negative terminal to the body/chassis?
Heat build up is really a non-issue under the hood of a car but a very considerable issue with our bikes, especially in casual street riding. I will stick a thermal probe one day between the frame and engine case to see what temperatures those wires really sit in during an average commute to work. The outside of my frame routinely gets too hot to touch and hold for more than a second or 2, especially in the summer.

I have a mate with a 2015 RSV4, same model as my Tuono. My bike has the hot start issue, his does not ? He has done 22,000km's with no issue, mine has done far less. Aprilia are replacing my starter motor & battery under warranty. I have two questions - 1. Is there an upgrade of the starter motor. 2. Why is there no hot start issue with some bikes & yet problems with others of the same year/model ?

I have a mate with a 2015 RSV4, same model as my Tuono. My bike has the hot start issue, his does not ? He has done 22,000km's with no issue, mine has done far less. Aprilia are replacing my starter motor & battery under warranty. I have two questions - 1. Is there an upgrade of the starter motor. 2. Why is there no hot start issue with some bikes & yet problems with others of the same year/model ?

For me it's only reeeealy hot. Like going under 30mph when it's 100 out for a long stretch or really beating it up on a pretty hot day and not waiting more than a minute or two to re start.

It could also be battery or stator for you, though stator is unlikely on that year.

Stator has been checked, regulator has been replaced, so we will see when the battery and starter motor have been replaced. Just strange that some bikes seem to suffer from this but not others ?

Kind of a crap shoot maybe. Some starters installed, or other various items, may be slightly more efficient. They would be less prone to failure under heat situations. It could also just be a matter of poor connector conductivity from one machine to the next. I'm going to troubleshoot the wiring on mine next, having only done the additional Positive wiring mod. I will add a similar Negative cable and test it, I will keep posting until I have mine solved.

Aprilia has used different starter motors and reduction gear ratios on the TV4 and RSV4 bikes from 2009 thru 2017. There are four different p/n starters, three different p/n starter reduction gears and two different sprag gears.

The RSV4 all use the larger, black color Denso starter motor.
The early TV4 can have the same Denso motor or a smaller grey color Mitsuba motor on later bikes.

The two starters require different reduction gears, #2 and #9 in diagram bellow.
Smaller Mitsuba starter motors on the TV4 use a 11/64 reduction gear and 50t sprag gear.
Denso starter motors use a 12/64 reduction and 49t sprag gear.

The starters and reduction gears can be interchanged and long as you match all three components.

Since there is no logical pattern as to what year or model V4 bikes experience the hot start issue, I wonder if there could be some miss matched parts on some bikes?